excuse my ignorance but what is the point of a chain tug anyway? Surely it can't be to keep the wheel in if both the chain breaks and the axle comes loose. It seems it wouldn't help keep tension in the chain either because it's not stopping the axle from moving forward in the dropout, which is what the chain wants the axle to do. Surely it also makes it slower to change a wheel.

My only thought would be if the hub axle had a hole in it for the screw in the chain tug to pull against. That way it would try and pull the hub back, keeping the tension of the chain up. Is this how it works?